Engine device

ABSTRACT

An engine device (1) including: an exhaust manifold (4) disposed on one of left and right sides of a cylinder head (2), and an intake manifold (3) disposed on another one of the left and right sides of the cylinder head (2). The engine device (1) further includes a turbocharger (30) that uses fluid energy of an exhaust gas discharged from the exhaust manifold (4) to compress fresh air to be flowed into the intake manifold (3). The turbocharger (30) is constituted by a two-stage turbocharger including a high-pressure turbocharger (51) coupled to the exhaust manifold (4) and a low-pressure turbocharger (52) coupled to the high-pressure turbocharger (51). The high-pressure turbocharger (51) is disposed on one of left and right lateral sides of the exhaust manifold (4), while the low-pressure turbocharger (52) is disposed above the exhaust manifold (4).

TECHNICAL FIELD

The present invention relates to an engine device including aturbocharger.

BACKGROUND ART

Conventinally, an engine device is equipped with a turbocharger thatuses exhaust energy to compress fresh air, in order to increase an airdensity in an engine cylinder, for the purpose of enhancing an engineoutput and improving a fuel efficiency (see Patent Literature 1 (PTL1)). In a diesel engine, a large amount of high-density air is suppliedinto a cylinder to combust a large amount of fuel, which can increase anengine output and an engine torque can be increased, and also canfacilitate mixing of the fuel and air to thereby reduce the amount ofNOx discharge with suppression of premix combustion.

Since a single-stage turbocharger including a single turbocharger has alimitation against requirement of a high-output engine, an engineequipped with a two-stage turbocharger in which two turbochargers of ahigh-pressure stage and a low-pressure stage are coupled in series hasbeen proposed (see Patent Literature 2 (PTL 2)).

CITATION LIST Patent Literature

PTL 1: Japanese Patent No. 4517550

PTL 2: Japanese Patent No. 5237785

SUMMARY OF INVENTION Technical Problem

An installation space for a diesel engine varies depending on a workvehicle (such as a construction machine or an agricultural machine) towhich the diesel engine is installed. Recently, due to demand for weightreduction and compactification, the installation space is oftenrestricted (confined). It therefore is necessary that component parts ofthe diesel engine are arranged in a compact layout. In addition to sucha problem of the restricted installation space, a structure with a highrigidity is required of a cylinder head because component parts such asan EGR device and a turbocharger are coupled to and supported by thecylinder head.

Arranging a high-pressure stage turbocharger and a low-pressure stageturbocharger of a two-stage turbocharger one above the other at aposition distant from an exhaust manifold as in an engine device of PTL2 results in a high moment exerted on an outlet of the exhaust manifoldwhich supports the two-stage turbocharger. Consequently, the two-stageturbocharger is supported with a lowered rigidity. In addition, a bypasspath provided on a turbine side of the high-pressure stage is externalpiping, and therefore a piping structure of the two-stage turbochargeris complicated, which makes assemblage to the engine device troublesome.

A technical problem of the present invention is to provide an enginedevice that is improved based on studies on the existing circumstancesas mentioned above.

Solution to Problem

An aspect of the present invention is an engine device including: anexhaust manifold and an intake manifold, the exhaust manifold beingdisposed on one of left and right sides of a cylinder head, the intakemanifold being disposed on the other of the left and right sides of thecylinder head; and a turbocharger that uses fluid energy of an exhaustgas discharged from the exhaust manifold, to compress fresh air to beflowed into the intake manifold, the turbocharger being constituted by atwo-stage turbocharger including a high-pressure turbocharger coupled tothe exhaust manifold and a low-pressure turbocharger coupled to thehigh-pressure turbocharger, the high-pressure turbocharger beingdisposed on one of left and right lateral sides of the exhaust manifold,the low-pressure turbocharger being disposed above the exhaust manifold.

The engine device may be configured such that: the high-pressureturbocharger includes a high-pressure turbine and a high-pressurecompressor, the high-pressure turbine being in communication with anexhaust gas outlet of the exhaust manifold, the high-pressure compressorbeing configured to supply compressed air to the intake manifold; thelow-pressure turbocharger includes a low-pressure turbine and alow-pressure compressor, the low-pressure turbine having an exhaust gasinlet that is in communication with an exhaust gas outlet of thehigh-pressure turbine through an exhaust relay pipe, the low-pressurecompressor having a fresh air outlet that is in communication with afresh air inlet of the high-pressure compressor through a fresh airrelay pipe; and the low-pressure compressor is disposed above thehigh-pressure turbine, the high-pressure compressor is disposed on oneof front and rear sides relative to the high-pressure turbine, and thelow-pressure turbine is disposed on the other of the front and rearsides relative to the low-pressure compressor.

The engine device may be configured such that: the exhaust manifold hasan exhaust gas outlet that discharges an exhaust gas, the exhaust gasoutlet being opened toward one of left and right lateral sides; thehigh-pressure turbine has an exhaust gas inlet that is opened toward theexhaust manifold, and has an exhaust gas outlet that is opened towardthe other of front and rear sides; the low-pressure turbine has anexhaust gas inlet that is opened downward, and has an exhaust gas outletthat is opened toward the other of front and rear sides; the exhaust gasoutlet of the exhaust manifold and the exhaust gas inlet of thehigh-pressure turbine that are opposed to each other are coupled, to fixthe high-pressure turbocharger on one of left and right lateral sides ofthe exhaust manifold; and the exhaust gas outlet of the high-pressureturbine is fixed to one end of the exhaust relay pipe having an L-shape,the exhaust gas inlet of the low-pressure turbine is fixed to the otherend of the exhaust relay pipe, and the low-pressure turbocharger isfixed above the high-pressure turbocharger.

The engine device may be configured such that: the high-pressurecompressor has a fresh air inlet that is opened toward one of front andrear sides, and has a fresh air outlet that is opened downward; thelow-pressure compressor has a fresh air inlet that is opened toward oneof front and rear sides, and has a fresh air outlet that protrudes fromone of left and right lateral sides and then is directed toward one offront and rear sides; and one end of the fresh air relay pipe having aU-shape is fixed to the fresh air inlet of the high-pressure compressor,and the other end of the fresh air relay pipe is coupled to the freshair outlet of the low-pressure compressor.

The engine device may be configured such that: a blow-by gasrecirculation device that takes a blow-by gas in is provided on thecylinder head, and a blow-by gas outlet disposed on one of front andrear sides of the blow-by gas recirculation device is coupled to an airsupply pipe through a recirculation hose, the air supply pipe beingcoupled to the fresh air inlet of the low-pressure compressor; and theair supply pipe is disposed between the fresh air relay pipe and thecylinder head.

The engine device may be configured such that: the exhaust gas outlet ofthe high-pressure turbine is provided with a turbine discharge hole, abypass hole, and a wastegate valve, the turbine discharge hole beingconfigured to discharge an exhaust gas for rotating a turbine wheel, thebypass hole allowing the exhaust gas inlet and the exhaust gas outlet tocommunicate with each other, the wastegate valve being configured toopen and close the bypass hole.

Advantageous Effects of Invention

In an aspect of the present invention, the high-pressure turbochargerwith a low capacity is disposed opposed to the exhaust manifold, whilethe low-pressure turbocharger with a high capacity is disposed above theexhaust manifold 4. This enables the exhaust manifold and the two-stageturbocharger to be compactly arranged in a space existing on a leftlateral side of the engine, and also enables a topmost portion of thetwo-stage turbocharger to be positioned lower than a topmost portion ofthe engine device. This can contribute to downsizing of the enginedevice. In addition, the low-pressure turbocharger can be disposed closeto the cylinder head to which the exhaust manifold is coupled, and thusthe two-stage turbocharger can be fixed with a high rigidity.

In an aspect of the present invention, the high-pressure turbine iscoupled to the exhaust manifold, and the high-pressure turbocharger issupported with a high rigidity. In this condition, the low-pressureturbine is coupled to an upper surface of the exhaust relay pipe whichis coupled to the high-pressure turbocharger. Thereby, the low-pressureturbocharger can be supported from below by the high-pressureturbocharger. Since the low-pressure turbocharger is installed close toa position above the exhaust manifold, the center of gravity of thelow-pressure turbocharger is in the vicinity of a position above theposition where the exhaust manifold is coupled to the high-pressureturbocharger. Accordingly, the two-stage turbocharger can be compactlysupported with a high rigidity in the vicinity of the engine device.

In an aspect of the present invention, the high-pressure compressor andthe low-pressure compressor are coupled by the U-shaped fresh air relaypipe, and a front portion of the low-pressure turbocharger can be fixedto the high-pressure turbocharger which is supported with a highrigidity by the exhaust manifold. The fresh air inlet and the fresh airoutlet of the low-pressure compressor are extended in the samedirection, and can be easily coupled to the air supply pipe which is incommunication with an air cleaner (not shown) and to the fresh air relaypipe, respectively. This configuration can enhance a workability inassembling.

In an aspect of the present invention, the air supply pipe is coupled tothe low-pressure turbocharger which is an upper component of thetwo-stage turbocharger, and is disposed close to the cylinder head.Thus, the distance between the air supply pipe and the blow-by gasrecirculation device disposed above the cylinder head can be shortened.This makes it possible to shorten the recirculation hose. Since the airsupply pipe is disposed in a space surrounded by the fresh air relaypipe and the cylinder head, the air supply pipe can be prevented frombeing damaged by an external force which may be applied in a couplingportion coupled to a resin pipe which is connected to the air cleaner(not shown).

In an aspect of the present invention, the exhaust gas outlet of thehigh-pressure turbine is provided with the turbine discharge hole andthe bypass hole that are arranged side-by-side. With this configuration,it is possible to set whether to perform a compression operation by thehigh-pressure turbocharger in accordance with a rotational frequency ofthe engine device. Accordingly, with efficient use of exhaust energy,the two-stage turbocharger can stabilize the amount of fresh air to besupplied to the combustion chamber, and can reduce the amount of bracksmoke discharge while increasing an engine output.

BRIEF DESCRIPTION OF DRAWINGS

[FIG. 1] A front view of an engine.

[FIG. 2] A rear view of the engine.

[FIG. 3] A left side view of the engine.

[FIG. 4] A right side view of the engine.

[FIG. 5] A top plan view of the engine.

[FIG. 6] A bottom plan view of the engine.

[FIG. 7] A perspective view of the engine as viewed from diagonallyfront.

[FIG. 8] A perspective view of the engine as viewed from diagonallyrear.

[FIG. 9] An enlarged perspective view of a cylinder head as viewed froman intake manifold side.

[FIG. 10] An exploded perspective view of the cylinder head as viewedfrom an exhaust manifold side.

[FIG. 11] Am exploded perspective view of the cylinder head as viewedfrom the intake manifold side.

[FIG. 12] A top plan view of the cylinder head.

[FIG. 13] A front view of the cylinder head.

[FIG. 14] A perspective cross-sectional view of the cylinder head and anEGR device.

[FIG. 15] A perspective cross-sectional view of the cylinder head andthe exhaust manifold.

[FIG. 16] A perspective cross-sectional view of a coupling portion ofthe cylinder head coupled to an EGR cooler.

[FIG. 17] A perspective cross-sectional view of the EGR device.

[FIG. 18] A top plan view of the EGR device.

[FIG. 19] An exploded perspective view of the EGR device.

[FIG. 20] An exploded view of the coupling portion of the cylinder headcoupled to the EGR cooler.

[FIG. 21] A cross-sectional view of the coupling portion of the cylinderhead coupled to the EGR cooler.

[FIG. 22] A left side view of the engine for illustrating arrangement ofa two-stage turbocharger.

[FIG. 23] An enlarged rear view of the engine.

[FIG. 24] An enlarged front view of the engine.

[FIG. 25] A left side view of the two-stage turbocharger.

[FIG. 26] A perspective view of the two-stage turbocharger.

[FIG. 27] A right side view of the two-stage turbocharger.

[FIG. 28] An exploded perspective view of a coolant pump.

[FIG. 29] A partial cross-sectional view of a coolant pump attachingportion.

DESCRIPTION OF EMBODIMENT

In the following, an embodiment of the present invention will bedescribed with reference to the drawings. First, referring to FIG. 1 toFIG. 8, an overall structure of a diesel engine (engine device) 1 willbe described. In the descriptions below, opposite side portions parallelto a crankshaft 5 (side portions on opposite sides relative to thecrankshaft 5) will be defined as left and right, a side where a flywheelhousing 7 is disposed will be defined as front, and a side where acooling fan 9 is disposed will be defined as rear. For convenience,these are used as a benchmark for a positional relationship of left,right, front, rear, up, and down in the diesel engine 1.

As shown in FIG. 1 to FIG. 8, an intake manifold 3 and an exhaustmanifold 4 are disposed in one side portion and the other side portionof the diesel engine 1 parallel to the crankshaft 5. In the embodiment,the intake manifold 3 provided on a right surface of a cylinder head 2is formed integrally with the cylinder head 2. The exhaust manifold 4 isprovided on a left surface of the cylinder head 2. The cylinder head 2is mounted on a cylinder block 6 in which the crankshaft 5 and a piston(not shown) are disposed.

The crankshaft 5 has its front and rear distal ends protruding fromfront and rear surfaces of the cylinder block 6. The flywheel housing 7is fixed to one side portion of the diesel engine 1 (in the embodiment,a front surface side of the cylinder block 6) intersecting thecrankshaft 5. A flywheel 8 is disposed in the flywheel housing 7. Theflywheel 8, which is pivotally supported on the front end side of thecrankshaft 5, is configured to rotate integrally with the crankshaft 5.The flywheel 8 is configured such that power of the diesel engine 1 isextracted to an actuating part of a work machine (for example, ahydraulic shovel, a forklift, or the like) through the flywheel 8. Thecooling fan 9 is disposed in the other side portion of the diesel engine1 (in the embodiment, a rear surface side of the cylinder block 6)intersecting the crankshaft 5. A rotational force is transmitted fromthe rear end side of the crankshaft 5 to the cooling fan 9 through aV-belt 10.

An oil pan 11 is disposed on a lower surface of the cylinder block 6. Alubricant is stored in the oil pan 11. The lubricant in the oil pan 11is suctioned by an oil pump (not shown) disposed on the right surfaceside of the cylinder block 6, the oil pump being arranged in a couplingportion where the cylinder block 6 is coupled to the flywheel housing 7.The lubricant is then supplied to lubrication parts of the diesel engine1 through an oil cooler 13 and an oil filter 14 that are disposed on theright surface of the cylinder block 6. The lubricant supplied to thelubrication parts is then returned to the oil pan 11. The oil pump (notshown) is configured to be driven by rotation of the crankshaft 5.

In the coupling portion where the cylinder block 6 is coupled to theflywheel housing 7, a fuel feed pump 15 for feeding a fuel is attached.The fuel feed pump 15 is disposed below an EGR device 24. A common rail16 is fixed to a side surface of the cylinder block 6 at a locationbelow the intake manifold 3 of the cylinder head 2. The common rail 16is disposed above the fuel feed pump 15. Injectors (not shown) for fourcylinders are provided on an upper surface of the cylinder head 2 whichis covered with a head cover 18. Each of the injectors has a fuelinjection valve of electromagnetic-controlled type.

Each of the injectors is connected to a fuel tank (not shown) throughthe fuel feed pump 15 and the common rail 16 having a cylindrical shape.The fuel tank is mounted in a work vehicle. A fuel in the fuel tank ispressure-fed from the fuel feed pump 15 to the common rail 16, so that ahigh-pressure fuel is stored in the common rail 16. By controlling theopening/closing of the fuel injection valves of the injectors, thehigh-pressure fuel in the common rail 16 is injected from the injectorsto the respective cylinders of the diesel engine 1.

A blow-by gas recirculation device 19 is provided on an upper surface ofthe head cover 18 covering intake and exhaust valves (not shown), etc.disposed on the upper surface of the cylinder head 2. The blow-by gasrecirculation device 19 takes in a blow-by gas that has leaked out of acombustion chamber of the diesel engine 1 or the like toward the uppersurface of the cylinder head 2. A blow-by gas outlet of the blow-by gasrecirculation device 19 is in communication with an intake part of atwo-stage turbocharger 30 through a recirculation hose 68. A blow-bygas, from which a lubricant component is removed in the blow-by gasrecirculation device 19, is then recirculated to the intake manifold 3via the two-stage turbocharger 30.

An engine starting starter 20 is attached to the flywheel housing 7. Theengine starting starter 20 is disposed below the exhaust manifold 4. Aposition where the engine starting starter 20 is attached to theflywheel housing 7 is below a coupling portion where the cylinder block6 is coupled to the flywheel housing 7.

A coolant pump 21 for smoothing a coolant is provided in a portion ofthe rear surface of the cylinder block 6, the portion being a littleleft-hand. The coolant pump 21 is disposed below the cooling fan 9.Rotation of the crankshaft 5 causes the coolant pump 21 as well as thecooling fan 9 to be driven through the cooling fan driving V-belt 10.Driving the coolant pump 21 causes a coolant in a radiator (not shown)mounted in the work vehicle to be supplied to the coolant pump 21. Thecoolant is then supplied to the cylinder head 2 and the cylinder block6, to cool the diesel engine 1.

A coolant inlet pipe 22 disposed below the exhaust manifold 4 isprovided on the left surface of the cylinder block 6 and is fixed at aheight equal to the height of the coolant pump 21. The coolant inletpipe 22 is in communication with a coolant outlet of the radiator. Acoolant outlet pipe 23 that is in communication with a coolant inlet ofthe radiator is fixed at a position above a rear surface of the cylinderhead 2. The cylinder head 2 has a coolant drainage 35 that protrudesrearward from the intake manifold 3. The coolant outlet pipe 23 isprovided on an upper surface of the coolant drainage 35.

The inlet side of the intake manifold 3 is coupled to an air cleaner(not shown) via a collector (EGR main body case) 25 of an EGR device 24(exhaust-gas recirculation device) which will be described later. Freshair (outside air) suctioned by the air cleaner is subjected to dustremoval and purification in the air cleaner, then fed to the intakemanifold 3 through the collector 25, and then supplied to the respectivecylinders of the diesel engine 1. In the embodiment, the collector 25 ofthe EGR device 24 is coupled to the right side of the intake manifold 3which is formed integrally with the cylinder head 2 to form the rightsurface of the cylinder head 2. That is, an outlet opening of thecollector 25 of the EGR device 24 is coupled to an inlet opening of theintake manifold 3 provided on the right surface of the cylinder head 2.In this embodiment, the collector 25 of the EGR device 24 is coupled tothe air cleaner via an intercooler (not shown) and the two-stageturbocharger 30, as will be described later.

The EGR device 24 includes: the collector 25 serving as a relay pipepassage that mixes a recirculation exhaust gas of the diesel engine 1(an EGR gas from the exhaust manifold 4) with fresh air (outside airfrom the air cleaner), and supplies a mixed gas to the intake manifold3; an intake throttle member 26 that communicates the collector 25 withthe air cleaner; a recirculation exhaust gas tube 28 that constitutes apart of a recirculation flow pipe passage connected to the exhaustmanifold 4 via an EGR cooler 27; and an EGR valve member 29 thatcommunicates the collector 25 with the recirculation exhaust gas tube28.

The EGR device 24 is disposed on the right lateral side of the intakemanifold 3 in the cylinder head 2. The EGR device 24 is fixed to theright surface of the cylinder head 2, and is in communication with theintake manifold 3 in the cylinder head 2. In the EGR device 24, thecollector 25 is coupled to the intake manifold 3 on the right surface ofthe cylinder head 2, and an EGR gas inlet of the recirculation exhaustgas tube 28 is coupled and fixed to a front portion of the intakemanifold 3 on the right surface of the cylinder head 2. The EGR valvemember 29 and the intake throttle member 26 are coupled to the front andrear of the collector 25, respectively. An EGR gas outlet of therecirculation exhaust gas tube 28 is coupled to the rear end of the EGRvalve member 29.

The EGR cooler 27 is fixed to the front surface of the cylinder head 2.The coolant and the EGR gas flowing in the cylinder head 2 flows intoand out of the EGR cooler 27. In the EGR cooler 27, the EGR gas iscooled. EGR cooler coupling bases 33, 34 for coupling the EGR cooler 27to the front surface of the cylinder head 2 protrude from left and rightportions of the front surface of the cylinder head 2. The EGR cooler 27is coupled to the coupling bases 33, 34. That is, the EGR cooler 27 isdisposed on the front side of the cylinder head 2 and at a positionabove the flywheel housing 7 such that a rear end surface of the EGRcooler 27 and the front surface of the cylinder head 2 are spaced fromeach other.

The two-stage turbocharger 30 is disposed on a lateral side (in theembodiment, the left lateral side) of the exhaust manifold 4. Thetwo-stage turbocharger 30 includes a high-pressure turbocharger 51 and alow-pressure turbocharger 52. The high-pressure turbocharger 51 includesa high-pressure turbine 53 in which a turbine wheel (not shown) isprovided and a high-pressure compressor 54 in which a blower wheel (notshown) is provided. The low-pressure turbocharger 52 includes alow-pressure turbine 55 in which a turbine wheel (not shown) is providedand a low-pressure compressor 56 in which a blower wheel (not shown) isprovided.

An exhaust gas inlet 57 of the high-pressure turbine 53 is coupled tothe exhaust manifold 4. An exhaust gas inlet 60 of the low-pressureturbine 55 is coupled to an exhaust gas outlet 58 of the high-pressureturbine 53 via a high-pressure exhaust gas tube 59. An exhaust gasintroduction side end portion of an exhaust gas discharge pipe (notshown) is coupled to an exhaust gas outlet 61 of the low-pressureturbine 55. A fresh air supply side (fresh air outlet side) of the aircleaner (not shown) is connected to a fresh air inlet port (fresh airinlet) 63 of the low-pressure compressor 56 via an air supply pipe 62. Afresh air inlet port 66 of the high-pressure compressor 54 is coupled toa fresh air supply port (fresh air outlet) 64 of the low-pressurecompressor 56 via a low-pressure fresh air passage pipe 65. A fresh airintroduction side of the intercooler (not shown) is connected to a freshair supply port 67 of the high-pressure compressor 54 via ahigh-pressure fresh air passage pipe 71.

The high-pressure turbocharger 51 is coupled to the exhaust gas outlet58 of the exhaust manifold 4, and is fixed to the left lateral side ofthe exhaust manifold 4. On the other hand, the low-pressure turbocharger52 is coupled to the high-pressure turbocharger 51 via the high-pressureexhaust gas tube 59 and the low-pressure fresh air passage pipe 65, andis fixed above the exhaust manifold 4. Thus, the exhaust manifold 4 andthe high-pressure turbocharger 51 with a small diameter are disposedside-by-side with respect to the left-right direction below thelow-pressure turbocharger 52 with a large diameter. As a result, thetwo-stage turbocharger 30 is arranged so as to surround the left surfaceand the upper surface of the exhaust manifold 4. That is, the exhaustmanifold 4 and the two-stage turbocharger 30 are arranged so as to forma rectangular shape in a rear view (or front view), and are compactlyfixed to the left surface of the cylinder head 2.

Next, referring to FIG. 9 to FIG. 16, a configuration of the cylinderhead 2 will be described. As shown in FIG. 9 to FIG. 16, the cylinderhead 2 is provided with a plurality of intake fluid passages 36 fortaking fresh air into a plurality of intake ports (not shown) and aplurality of exhaust fluid passages 37 for emitting an exhaust gas froma plurality of exhast ports. The intake manifold 3 which aggregates theplurality of intake fluid passages 36 is formed integrally with a rightside portion of the cylinder head 2. Since the cylinder head 2 isintegrated with the intake manifold 3, a gas sealability between theintake manifold 3 and the intake fluid passages 36 can be enhanced, andin addition, the rigidity of the cylinder head 2 can be increased.

The cylinder head 2 is configured such that the exhaust manifold 4 iscoupled to the left surface of the cylinder head 2 which is opposite tothe right surface where the intake manifold 3 is provided, and the EGRcooler 27 is coupled to the front surface (a surface on the flywheelhousing 7 side) of the cylinder head 2 which is adjacent to the left andright surfaces. Coupling bases (EGR cooler coupling bases) 33, 34 towhich the EGR cooler 27 is coupled are provided so as to protrude fromthe front surface of the cylinder head 2. The coupling bases 33, 34 areprovided therein with EGR gas fluid passages (EGR gas relay fluidpassages) 31, 32 and coolant passages (coolant relay fluid passages) 38,39.

Since the EGR gas relay fluid passages 31, 32 and the coolant passages38, 39 are provided in the coupling bases 33, 34 to which the EGR cooler27 is coupled, it is not necessary that coolant piping and EGR gaspiping are disposed between the EGR cooler 27 and the cylinder head 2.This can give a sealability to a coupling portion coupled to the EGRcooler 27 without any influence of, for example, extension andcontraction of piping caused by the EGR gas or the coolant. This canalso enhance a resistance (structural stability) against externalfluctuation factors such as heat and vibration, and moreover can makethe configuration compact.

The cylinder head 2 includes an upstream EGR gas relay fluid passage 31through which a front portion of the left surface is in communicationwith the front surface. An EGR gas outlet 41 disposed at the front endof the exhaust manifold 4 is in communication with the upstream EGR gasrelay fluid passage 31. The cylinder head 2 also includes a downstreamEGR gas relay fluid passage 32 through which a front portion of theright surface (on the front side of the intake manifold 3) is incommunication with the front surface. The EGR gas inlet of therecirculation exhaust gas tube 28 is in communication with thedownstream EGR gas relay fluid passage 32. The cylinder head 2 has theEGR cooler coupling bases 33, 34 which are formed by left and rightedges of the front surface of the cylinder head 2 (a front-left cornerportion and a front-right corner portion of the cylinder head 2) beingprotruded frontward. The upstream EGR gas relay fluid passage 31 isprovided inside the coupling base 33, and the downstream EGR gas relayfluid passage 32 is provided inside the coupling base 34.

The EGR device 24 is coupled to the intake manifold 3 which is providedon the right surface of the cylinder head 2 so as to protrude therefrom.The intake manifold 3 is disposed in a portion of the right surface ofthe cylinder head 2, the portion being relatively close to the rear side(the cooling fan 9 side). The intake manifold 3 is formed by a lowerportion of the right surface of the cylinder head 2 being protrudedrightward. The intake manifold 3 has an intake inlet 40 at its middleportion with respect to the front-rear direction. An intake outlet 83 ofthe collector 25 of the EGR device 24 is coupled to the intake inlet 40of the intake manifold 3 which protrudes from the right surface of thecylinder head 2, and the EGR device 24 is fixed to the right lateralside of the cylinder head 2.

On the front side (the flywheel housing 7 side) of the right surface ofthe cylinder head 2, the coupling base 34 coupled to the EGR cooler 27protrudes frontward, and an EGR gas outlet of the downstream EGR gasrelay fluid passage 32 is opened in a right surface of the coupling base34. One end of the recirculation exhaust gas tube 28 of the EGR device24 is coupled to the right surface of the coupling base 34, and therebythe collector 25 of the EGR device 24 is in communication with thedownstream EGR gas relay fluid passage 32 provided inside the cylinderhead 2 via the recirculation exhaust gas tube 28 and the EGR valvemember 29.

On the rear side (the cooling fan 9 side) of the right surface of thecylinder head 2, the coolant drainage (thermostat case) 35 whose uppersurface is opened to communicate with a coolant outlet pipe (thermostatcover) 23 protrudes rearward, and a thermostat (not shown) is installedtherein. The coolant drainage 35 is offset at the rear of the rightsurface of the cylinder head 2, and therefore it is possible that theV-belt 10 wound on a fan pulley 9 a to which the cooling fan 9 is fixedextends through a space below the coolant drainage 35. Thus, the lengthof the diesel engine 1 in the front-rear direction can be shortened. Thecoolant drainage 35 also protrudes from the right surface of thecylinder head 2. On the right surface of the cylinder head 2, the intakemanifold 3 and the coolant drainage 35 are arranged one behind the otherwith respect to the front-rear direction.

On the front side (the flywheel housing 7 side) of the left surface ofthe cylinder head 2, the coupling base 33 coupled to the EGR cooler 27protrudes frontward, and an EGR gas inlet 96 of the upstream EGR gasrelay fluid passage 31 is opened in a left surface of the coupling base33. That is, in the left surface of the cylinder head 2, the EGR gasinlet 96 of the upstream EGR gas relay fluid passage 31 and exhaust gasoutlets of the plurality of exhaust fluid passages 37 are arranged inthe front-rear direction, and are opened. The exhaust manifold 4 has, inits right surface which is coupled to the left surface of the cylinderhead 2, the EGR gas outlet 41 which is in communication with theupstream EGR gas relay fluid passage 31 and exhaust gas inlets 42 whichare in communication with the plurality of exhaust fluid passages 37 arearranged in the front-rear direction, and are opened. Since the EGRinlet and the exhaust gas outlets are arranged side-by-side in the samesurface of the cylinder head 2, it is easy for a coupling portion wherethe cylinder head 2 is coupled to the exhaust manifold 4 to obtain anairtightness (gas sealability) by sandwiching a single gasket 45therebetween.

The exhaust manifold 4 is provided therein with an exhaust aggregatepart 43 which is in communication with the EGR gas outlet 41 and theexhaust gas inlets 42. The exhaust aggregate part 43 is disposed suchthat its longitudinal direction is parallel to the front-rear direction.An exhaust gas outlet 44 which is in communication with the exhaustaggregate part 43 is opened in a rear portion of the left surface of theexhaust manifold 4. The exhaust manifold 4 is configured such that,after an exhaust gas coming from the exhaust fluid passages 37 of thecylinder head 2 flows into the exhaust aggregate part 43 via the exhaustgas inlets 42, part of the exhaust gas serves as an EGR gas and flowsinto the upstream EGR gas relay fluid passage 31 of the cylinder head 2via the EGR gas outlet 41 while the rest of the exhaust gas flows intothe two-stage turbocharger 30 via the exhaust gas outlet 44.

On the front surface of the cylinder head 2, the left and right pair ofEGR cooler coupling bases 33, 34 are disposed on the exhaust manifold 4side and on the intake manifold 3 side, respectively. The EGR coolercoupling base 33 has the upstream EGR gas relay fluid passage 31 throughwhich the EGR gas fluid passage of the exhaust manifold 4 communicateswith the EGR gas fluid passage of the EGR cooler 27. The EGR coolercoupling base 34 has the downstream EGR gas relay fluid passage 32through which the EGR gas fluid passage of the EGR device 24communicates with the EGR gas fluid passage of the EGR cooler 27. TheEGR cooler coupling base 33 also has the downstream coolant passage 38to which a coolant is discharged from the EGR cooler 27. The EGR coolercoupling base 34 has the upstream coolant passage 39 that supplies acoolant to the EGR device 24 and to the EGR cooler 27.

Since the EGR cooler coupling bases 33, 34 are configured in aprotruding manner, there is no need for EGR gas piping that communicatesthe exhaust manifold 4, the EGR cooler 27, and the EGR device 24. Thus,the number of coupling portions of the EGR gas fluid passage is small.Accordingly, in the diesel engine 1 that aims to reduce NOx by the EGRgas, EGR gas leakage can be reduced, and moreover deformation can besuppressed which may otherwise be caused by a change in a stress due toextension and contraction of piping. Since the EGR gas relay fluidpassages 31, 32 and the coolant passages 38, 39 are provided in the EGRcooler coupling bases 33, 34, the shapes of the fluid passages 31, 32,38, 39 formed in the cylinder head 2 are simplified, so that thecylinder head 2 can be easily formed by casting without using acomplicated core.

The EGR cooler coupling base 33 on the intake manifold 3 side and theEGR cooler coupling base 34 on the exhaust manifold 4 side are distantfrom each other. This can suppress a mutual influence between thermaldeformations of the coupling bases 33, 34. Accordingly, gas leakage anddamage of coupling portions where the EGR cooler coupling bases 33, 34are coupled to the EGR cooler 27 can be prevented, and in addition, abalance of the rigidity of the cylinder head 2 can be maintained.Moreover, the volume of the front surface of the cylinder head 2 can bereduced, which leads to weight reduction of the cylinder head 2.Furthermore, it is possible that the EGR cooler 27 is disposed at adistance from the front surface of the cylinder head 2, to provide aspace on the front and rear siddes of the EGR cooler 27. This enablescool air to flow around the EGR cooler 27, thus increasing the coolingefficiency of the EGR cooler 27.

In the EGR cooler coupling base 33, the downstream coolant passage 38 isdisposed above the upstream EGR gas relay fluid passage 31. In the EGRcooler coupling base 34, the downstream EGR gas relay fluid passage 32is disposed above the upstream coolant passage 39. A coolant inlet ofthe downstream coolant passage 38 and an EGR gas inlet of the downstreamEGR gas relay fluid passage 32 are disposed at the same height. Acoolant outlet of the upstream coolant passage 39 and an EGR gas outletof the downstream EGR gas relay fluid passage 32 are disposed at thesame height.

Since the EGR gas relay fluid passages 31, 32 and the coolant passages38, 39 are provided in the EGR cooler coupling bases 33, 34 protrudingat a distance from each other, a mutual influence between thermaldeformations of the EGR cooler coupling bases 33, 34 is relieved. In theEGR cooler coupling bases 33, 34, the EGR gas flowing in the EGR gasrelay fluid passages 31, 32 is cooled by the coolant flowing in thecoolant passages 38, 39, so that thermal deformations of the EGR coolercoupling bases 33, 34 are suppressed. In addition, the up-downpositional relationship of the EGR gas relay fluid passages 31, 32 andthe coolant passages 38, 39 in one of the EGR cooler coupling bases 33,34 is reverse to that in the other of the EGR cooler coupling bases 33,34. As a result, heat distributions in the respective EGR coolercoupling bases 33, 34 are in opposite directions with respect to theup-down direction, which can reduce an influence of thermal deformationin the height direction in the cylinder head 2.

An outer peripheral wall of the cylinder head 2 stands upward at aperipheral edge of the upper surface of the cylidner head 2, to providea spacer 46 which is coupled to a peripheral edge of a lower surface ofthe head cover 18. The spacer 46 has, in a right surface thereof, aplurality of openings 47. Fuel pipes 48 which couple injectors (notshown) provided in the cylinder head 2 to the common rail 16 passthrough the openings 47. Since the spacer 46 integrated with thecylinder head 2 is disposed above the cylinder head 2, the rigidity ofthe cylinder head 2 is increased, which can reduce distortion of thecylinder head 2 itself and also can allow component parts coupled to thecylinder head 2 to be supported with a high rigidity.

A configuration of the EGR device 24 will now be described withreference to FIG. 9 to FIG. 11, FIG. 14, FIG. 15, and FIG. 17 to FIG.19. As shown in FIG. 9 to FIG. 11, FIG. 14, FIG. 15, and FIG. 17 to FIG.19, the EGR device 24 includes the collector (main body case) 25 thatmixes fresh air with an EGR gas, and supplies a mixture to the intakemanifold 3. The intake manifold 3 and the intake throttle member 26 fortaking fresh air in are connected in communication with each other viathe collector 25. The EGR valve member 29 which leads to an outlet sideof the recirculation exhaust gas tube 28 is connected in communicationwith the collector 25.

In the collector 25, a fresh air flow direction and an EGR gas flowdirection cross each other perpendicularly or with a obtuse angle, and adirection in which a mixed gas of the EGR gas and the fresh air is takeninto the intake manifold 3 intersects each of the fresh air flowdirection and the EGR gas flow direction. A fresh air inlet 81 to whichthe fresh air is supplied is opened in one of front and rear surfaces ofthe collector 25, whereas an EGR gas inlet 82 to which the EGR gas issupplied is opened in the other of the front and rear surfaces of thecollector 25. The intake outlet 83 which is coupled to the intakemanifold 3 is opened in a left surface of the collector 25. The EGR gasinlet 82 and the intake outlet 83 are disposed at the same height, andthe fresh air inlet 81 and the EGR gas inlet 82 are disposed atdifferent heights.

In the collector 25, fresh air taken from the intake throttle member 26into the fresh air inlet 81 flows in the front-rear direction and thenin the up-down direction while curving in an L-shape, whereas an EGR gastaken from the EGR valve member 29 into the EGR gas inlet 82 flowsobliquely upward. As a result, the EGR gas flows in toward a flow of thefresh air, which facilitates mixing of the EGR gas with the fresh air.The mixed gas of the fresh air and the EGR gas flows in the up-downdirection and then in the left-right direction while curving in anL-shape, to flow into the intake manifold 3 through the intake outlet83. A direction in which the mixed gas is emitted intersects not onlythe directions in which the fresh air and the EGR gas are taken in butalso the directions in which the fresh air and the EGR gas flow withinthe collector 25. Consequently, a distribution of mixture of the EGR gaswith the fresh air can be made uniformed.

In the collector 25, as described above, the EGR gas flow direction isat an angle of 90° or more relative to the fresh air flow direction, andthe fresh air flow and the EGR gas flow intersect each other, so that adistribution of mixture of the EGR gas with the fresh air can be madeuniform, and an uneven flow of the EGR gas in the intake manifold 3 canbe suppressed. As a result, a concentration of the intake EGR gassupplied to each of the plurality of intake fluid passages 36 of thecylinder head 2 can be made uniform. Thus, a variation in combustionaction among cylinders of the diesel engine 1 can be suppressed.Consequently, generation of brack smoke is suppressed, and the amount ofNOx can be reduced while a good combustion state of the diesel engine 1is maintained. That is, purifying (cleaning) the exhaust gas by arecirculation flow of the EGR gas can be achieved without causing amisfire in a specific cylinder.

The collector 25 includes an upper case (first case) 84 with the freshair inlet 81 and a lower case (second case) 85 with the EGR gas inlet 82and the intake outlet 83 being coupled to each other. Since thecollector 25 is divisible in the up-down direction into the upper case84 and the lower case 85, a mixed fluid passage where the EGR gas flowand the fresh air flow intersect each other at an angle of 90° or morecan be easily formed in the collector 25. It therefore is possible thatthe collector 25 is formed as a casting with a high rigidity, andmoreover, weight reduction of the collector 25 can be obtained byforming the collector 25 as an aluminium-based casting product.

The upper case 84 is provided therein with a downstream EGR gas fluidpassage (first EGR gas fluid passage) 86 a which is a part of the EGRgas fluid passage 86 where the EGR gas flows and a mixing chamber 87 inwhich the fresh air and the EGR gas are mixed. The lower case 85 isprovided therein with an upstream EGR gas fluid passage (second EGR gasfluid passage) 86 b through which the downstream EGR gas fluid passage86 a is in communication with the EGR gas inlet 82 and a mixed gas fluidpassage 88 through which a mixed gas obtained by mixing the fresh airwith the EGR gas is supplied from the mixing chamber 87 to the intakemanifold 3.

The EGR gas inlet 82 is disposed in the lower case 85 while the freshair inlet 81 and the mixing chamber 87 are disposed in the upper case84. In the mixing chamber 87, therefore, the fresh air flowing from thefresh air inlet 81 and the EGR gas flowing from the lower case 85intersect each other, so that the fresh air and the EGR gas can beefficiently mixed. In addition, the intake outlet 83 is disposed in thelower case 85, and the fresh air having entered the upper case 84 tendsto flow toward the lower case 85. As a result, mixing of the EGR gasflowing toward the upper case 84 with the fresh air is made uniform.Furthermore, each of the EGR gas fluid passage 86, the mixing chamber87, and the mixed gas fluid passage 88 can be compactly configuredwithin the collector 25, and thus the collector 25 can be downsized.

In a plan view, the downstream EGR gas fluid passage 86 a is coupledwith an offset to a side surface (right side surface) of the mixingchamber 87 opposite to a side surface (left side surface) thereof havingthe intake outlet 83 relative to a central axis of the mixing chamber87, and the downstream EGR gas fluid passage 86 a and the upstream EGRgas fluid passage 86 b are in communication with each other so that theEGR gas fluid passage 86 is formed in a spiral manner. The EGR gas fluidpassage 86 composed of the downstream EGR gas fluid passage 86 a and theupstream EGR gas fluid passage 86 b has a bent shape curved toward theside (right side) opposite to the intake outlet 83 in a plan view. Abottom of the upstream EGR gas fluid passage 86 b is constituted by aslope (a slope inclined upward toward the rear) extending from the EGRgas inlet 82 toward the upper case 84.

A portion of the mixing chamber 87 that is in communication with the EGRgas fluid passage 86 is on the side opposite to the intake outlet 83.The EGR gas flowing into the mixing chamber 87, therefore, reaches theintake outlet 83 while being guided by a fresh air flow, which allowsthe EGR gas to be uniformly mixed with the fresh air. The EGR gasflowing from the EGR gas fluid passage 86 into the mixing chamber 87flows in a direction against the direction from the mixing chamber 87toward the mixed gas fluid passage 88. This causes the fresh air and theEGR gas to collide with each other while flowing within the mixingchamber 87. Accordingly, the EGR gas is smoothly mixed with the freshair.

Since the EGR gas flows along the EGR gas fluid passage 86 having aspiral shape, the EGR gas creates a swirling flow having a clockwisevortex when flowing into the mixing chamber 87. Such a turbulent EGR gasflows in a direction against the fresh air gas flow. Thus,simultaneously with flowing into the mixing chmber 87, the EGR gas issmoothly mixed with the fresh air flowing within the mixing chamber 87.In the collector 25, therefore, the fresh air and the EGR gas can beefficiently mixed (the EGR gas can be smoothly dispersed in the mixedgas) by agitation before they are fed to the intake manifold 3, so thata variation (unevenness) in the gas mixing state within the collector 25can be suppressed more reliably. As a result, a mixed gas having lessunevenness can be distributed to the respective cylinders of the dieselengine 1, and a variation in the EGR gas amount among the cylinders canbe suppressed. Accordingly, it is possible to suppress generation ofbrack smoke, and to reduce the amount of NOx while maintaining a goodcombustion state of the diesel engine 1. In addition, the EGR gas fluidpassage 86 having a spiral shape gives sufficient swirling properties tothe EGR gas flowing into the mixing chamber 87. Thus, the collector 25can be shaped with a shortened length in the front-rear direction.

A lower surface flange 84 a of the upper case 84 and an upper surfaceflange 85 a of the lower case 85 are fastened with bolts, to form thecollector 25 having openings (the fresh air inlet 81, the EGR gas inlet82, and the intake outlet 83) in three directions (toward the front,rear, and left). The upper case 84 has a rear surface flange 84 b inwhich the fresh air inlet 81 is opened, and a fresh air outlet of theintake throttle member 26 is fastened to the rear surface flange 84 bwith bolts. The intake throttle member 26 adjusts the degree of openingof an intake valve (butterfly valve) 26 a provided therein, to therebyadjust the amount of fresh air supply to the collector 25.

The lower case 85 has a front surface flange 85 b in which the EGR gasinlet 82 is opened, and an EGR gas outlet of the EGR valve member 29 isfastened with bolts to the front surface flange 85 b with interpositionof a relay flange 89 having a rectangular pipe shape. The EGR valvemember 29 adjusts the degree of opening of an EGR valve (not shown)provided therein, to thereby adjust the amount of EGR gas supply to thecollector 25. A reed valve 90 inserted in the EGR gas inlet 82 is fixedinside the front surface flange 85 b of the lower case 85. The relayflange (spacer) 89 which is fastened to the front surface flange 85 bwith bolts covers the front side of the reed valve 90. As a result, thecollector 25 is provided therein with the reed valve 90 disposed in aportion of the EGR gas fluid passage 86, the portion being on the EGRgas inlet 82 side.

The relay flange 89 has, in its rear surface coupled to the collector25, an EGR gas outlet 89 a which is in communication with the EGR gasinlet 82. The relay flange 89 has a front surface from which valvecoupling bases 89 b, 89 c to be coupled to the EGR valve member 29protrude. Openings of the valve coupling bases 89 b, 89 c are incommunication with the EGR gas outlet of the EGR valve member 29. In therelay flange 89, the EGR gas is merged at EGR gas inlets of the upperand lower valve coupling bases 89 b, 89 c, and then is caused to flowfrom the EGR gas inlet 82 into the EGR gas fluid passage 86 providedinside the collector 25 via the reed valve 90.

The EGR valve member 29 is configured such that: a valve body 29 e hasan EGR gas fluid passage 29 f in which an EGR valve (not shown) isdisposed; an actuator 29 d for adjusting the degree of opening of theEGR valve is disposed above the valve body 29 e; the EGR valve member 29has its longitudinal direction in parallel to the up-down direction; andthe EGR valve member 29 is coupled to the front side of the collector 25with interposition of the relay flange 89. The EGR valve member 29 has,in a rear surface of the valve body 29 e which is arranged lower, outletside flanges 29 a, 29 b to be coupled respectively to the valve couplingbases 89 b, 89 c of the relay flange 89. The outlet side flanges 29 a,29 b are arranged one above the other. The EGR valve member 29 also has,in its front surface, an inlet side flange 29 c having an EGR gas inletthat is in communication with the EGR gas outlet of the recirculationexhaust gas tube 28.

The EGR valve member 29 is configured such that: after an EGR gas cooledby the EGR cooler 27 flows into the EGR gas inlet of the inlet sideflange 29 c through the downstream EGR gas relay fluid passage 32 of theEGR cooler coupling base 34 and the recirculation exhaust gas tube 28,the EGR gas is disbributed to upper and lower parts via the EGR gasfluid passage 29 f of the valve body 29 e. The EGR gas flow distributedto upper and lower parts through the EGR gas fluid passage 29 f is thensubjected to a flow rate adjustment by the EGR valve, and then entersthe relay flange 89 through the EGR gas outlets of the upper and loweroutlet side flanges 29 a, 29 b.

The recirculation exhaust gas tube 28 includes a gas pipe portion 28 aand a rib 28 b, the gas pipe portion 28 a being bent to have an L-shapein a plan view, the rib 28 b having a flat-plate shape protruding froman inner peripheral side of an outer wall of the gas pipe portion 28 a.The recirculation exhaust gas tube 28 has, at one end (rear end) of thegas pipe portion 28 a, an outlet side flange 28 c to be coupled to theinlet side flange 29 c of the EGR valve member 29, and also has, at theother end (left end) of the gas pipe portion 28 a, an inlet side flange28 d to be coupled to the right surface of the EGR cooler coupling base34. The recirculation exhaust gas tube 28 further has, in an uppersurface of a bent portion of the gas pipe portion 28 a, a sensorattachment base 28 e to which an EGR gas temperature sensor is attached.

In the EGR device 24, the collector 25 can be configured with ashortened length, and therefore the distance between the EGR valvemember 29 and the intake throttle member 26 can be shortened, whichenables the length of the EGR device 24 in the front-rear direction tobe shortened. In the EGR valve member 29, the actuator 29 d is disposedon the upper side. It therefore is possible that topmost portions of theEGR valve member 29, the collector 25, and the intake throttle member 26are at the same height. This can lower the height of the EGR device 24in the up-down direction, and also can narrow the width of the EGRdevice 24 in the left-right direction. Since the EGR device 24 can beconfigured compactly, coupling the EGR device 24 to the right side ofthe cylinder head 2 integrated with the intake manifold 3 can be easilyimplemented merely by adjusting the recirculation exhaust gas tube 28.In addition, such a configuraiton contributes to downsizing of thediesel engine 1.

The recirculation exhaust gas tube 28 has the flat-plate rib 28 b thatis coupled so as to connect the opposite ends of the gas pipe portion 28a. This gives a high rigidity to the recirculation exhaust gas tube 28,and also increases a strength with which the front end side of the EGRdevice 24 is supported on the cylinder head 2. In addition, therecirculation exhaust gas tube 28 has the flat-plate rib 28 b that isdisposed along an EGR gas fluid passage 28 f provided inside the gaspipe portion 28 a. Due to the rib 28 b, the gas pipe portion 28 a has awide heat dissipation area, which increases the effect of cooling theEGR gas flowing in the EGR gas fluid passage 28 f. This contributes tocooling a mixed gas prepared in the EGR device 24, and exerts an effectthat reduction in the amount of NOx generated from the mixed gas can beeasily kept in a proper state.

A configuration of the EGR cooler 27 will now be described withreference to FIG. 9 to FIG. 11, FIG. 13 to FIG. 16, and FIG. 20 to FIG.21. As shown in FIG. 9 to FIG. 11, FIG. 13 to FIG. 16, and FIG. 20 toFIG. 21, the EGR cooler 27 includes a heat exchanger 91 and a pair ofleft and right flange portions 92, 93. The heat exchanger 91 has acoolant passage and an EGR gas fluid passage alternately stacked. Thepair of left and right flange portions 92, 93 are disposed in left andright end portions of one side surface of the heat exchanger 91. Thecoolant outlet 94 is disposed in one of the left and right flangeportions 92, 93, while the coolant inlet 95 is disposed in the other ofthe left and right flange portions 92, 93. The EGR gas inlet 96 isdisposed in one of the left and right flange portions 92, 93, while theEGR gas outlet 97 is disposed in the other of the left and right flangeportions 92, 93. The left and right flange portions 92, 93 are coupledto the front surface of the cylinder head 2, so that the EGR cooler 27is fixed to the cylinder head 2.

Since each of the pair of left and right flange portions 92, 93 has acoolant opening and an EGR gas opening, it is possible that the flangeportions 92, 93 are made from a common member, and moreover materialcosts of the flange portions 92, 93 can be suppressed. The flangeportions 92, 93 are formed by a flat plate being bored to have throughholes 100 to 103 corresponding to the coolant and the EGR gas, the flatplate being coupled to the cylinder head 2. Thus, forming the flangeportions 92, 93 in the EGR cooler 27 is easy. In addition, a couplingportion where the flange portions 92, 93 are coupled to the heatexchanger 91 can be minimized, so that the amount of heat transfer fromthe cylinder head 2 to the heat exchanger 91 can be reduced, whichincreases the effect of cooling the EGR gas by the heat exchanger 91.

Since the EGR cooler 27 has the flange portions 92, 93 protruding fromthe rear surface of the heat exchanger 91, a space is formed between theheat exchanger 91 and the cylinder head 2. As a result, the EGR cooler27 is in a state where a wide area of the front and rear surfaces of theheat exchanger 91 is exposed to outdoor air. Heat dissipation occurs inthe heat exchanger 91, too. Thus, the effect of cooling the EGR gas bythe EGR cooler 27 is increased. This configuration can reduce the degreeof stacking in the heat exchanger 91 as compared to a configuration inwhich the rear surface and the front surface of the heat exchanger 91are attached. The length of the EGR cooler 27 in the front-direction canbe shorted, and thus the diesel engine 1 can be downsized.

The left flange portion 92 has the coolant outlet 94 and the EGR gasinlet 96, while the right flange portion 93 has the coolant inlet 95 andthe EGR gas outlet 97. In the left flange portion 92, the coolant outlet94 is disposed above the EGR gas inlet 96, while in the right flangeportion 93, the EGR gas outlet 97 is disposed above the coolant inlet95. The coolant outlet 94 and the EGR gas outlet 97 are disposed at thesame height, while the coolant inlet 95 and the EGR gas inlet 96 aredisposed at the same height.

The left and right flange portions 92, 93 of the EGR cooler 27 arecoupled respectively to the EGR cooler coupling bases 33, 34 protrudingfrom the front surface of the cylinder head 2. The upstream EGR gasrelay fluid passage 31 and the downstream coolant passage 38 of the leftEGR cooler coupling base 33 are in communication with the EGR gas inlet96 and the coolant outlet 94 of the left flange portion 92,respectively. The downstream EGR gas relay fluid passage 32 and theupstream coolant passage 39 of the right EGR cooler coupling base 34 arein communication with the EGR gas outlet 97 and the coolant inlet 95 ofthe right flange portion 93, respectively.

The EGR gas relay fluid passages 31, 32 and the coolant passages 38, 39are provided in the coupling bases 33, 34 to which the flange portions92, 93 of the EGR cooler 27 are coupled, and are in communication withthe EGR gas inlet and outlet 96, 97 and the coolant outlet and inlet 94,95 of the flange portions 92, 93. It is not necessary that coolantpiping and EGR gas piping are disposed between the EGR cooler 27 and thecylinder head 2. Accordingly, a sealability can be given to a couplingportion where the EGR cooler 27 and the cylinder head 2 are coupled toeach other without any influence of, for example, extension andcontraction of piping caused by the EGR gas or the coolant. In addition,the EGR cooler 27 is given an enhanced resistance against externalfluctuation factors such as heat and vibration, and can be compactlyinstalled in the cylinder head 2.

The coolant outlet 94 is disposed above the EGR gas inlet 96 in theflange portion 92, while the EGR gas outlet 97 is disposed above thecoolant inlet 95 in the flange portion 93. Thus, the flange portions 92,93 having identical shapes with their postures mutually upside-down areattached to the heat exchanger 91. This can reduce the number of typesof component parts included in the EGR cooler 27, thus improving anassemblability of the EGR cooler 27 and reducing costs of the componentparts.

The flange portion 92 is provided with the coolant outlet 94 and the EGRgas inlet 96 through which a coolant or an EGR gas having a largequantity of heat passes, while the flange portion 93 is provided withthe coolant inlet 95 and the EGR gas outlet 97 through which a coolantor an EGR gas having a small quantity of heat passes. Accordingly,distortion caused by thermal deformation of each of the flange portions92, 93 can be suppressed. In addition, the flange portions 92, 93 areconfigured as separate members whose thermal deformation is lessinfluential to each other, and therefore damage and breakdown of the EGRcooler 27 can be prevented.

In the EGR cooler 27, the coolant outlet 94 and the coolant inlet 95 aredisposed at diagonal positions, and the EGR gas inlet 96 and the EGR gasoutlet 97 are disposed at diagonal positions in a rear view. Since EGRgases having different quantities of heat and coolants having differentquantities of heat are respectively supplied or discharged at diagonalpositions, thermal deformations of coupling portions where the EGRcooler 27 is coupled to the cylinder head 2 can be mutually relieved, sothat deflection or slackness of the coupling portions can be suppressed.Accordingly, leakage of an EGR gas or a coolant in the EGR cooler 27 andin the cylinder head 2 can be prevented, and moreover a decrease in thecoupling strength can be prevented.

A plate-shaped gasket 98 is sandwiched between the cylinder head 2 andthe flange portions 92, 93 so as to extend across the left and rightflange portions 92, 93. A coolant inlet and a coolant outlet of thecylinder head 2, which are respectively in communication with thecoolant outlet 94 and the coolant inlet 95 of the flange portions 92,93, have O-rings 99 embedded therein, the O-rings 99 being ring-shapedseal members. The O-rings 99 are covered with the flange portions 92,93.

Since the flange portions 92, 93 configured as separate members arecoupled to the coupling bases 33, 34 of the cylinder head 2 with thegasket 98 interposed therebetween, a tension is exerted on the gasket 98due to thermal deformation of the coupling portion coupled to thecylinder head 2. This enhances a sealability (hermetic sealingperformance) of the gasket 98 in a coupling portion of each of the EGRgas inlet 96 and the EGR gas outlet 97. Thus, leakage of an EGR gasflowing from one to the other between the cylinder head 2 and the EGRcooler 27 can be prevented. The O-rings 99 are embedded in spacesdefined by rear end surfaces of the flange portions 92, 93 and thecoolant inlet and the coolant outlet of the coupling bases 33, 34 of thecylinder head 2. When a coolant flows, therefore, the coolant is incontact with the O-rings 99 in communication portions where the couplingbases 33, 34 are in communication with the flange portions 92, 93. Thus,a sealability (hermetic sealing performance) of the coupling portions ofthe coolant outlet and inlet 94, 95 can be obtained. Accordingly, eventhough the EGR cooler 27 where a liquid and a gas enter and exit iscoupled to the cylinder head 2, a sealability for each of the liquid andthe gas can be obtained, so that leakage of each of the EGR gas and thecoolant can be prevented.

An outer peripheral portion of each of the flange portions 92, 93 isbored to have through holes 100 for bolt fastening, at outer positions.Specifically, the left flange portion 92 has five through holes 100disposed in its upper, lower, and left sides, and the right flangeportion 93 has five through holes 100 disposed in its upper, lower, andright sides. Since the left flange portion 92 has the through holes 100disposed above the coolant outlet 94, below the EGR gas inlet 96, and tothe left of a portion between the coolant outlet 94 and the EGR gasinlet 96, a sealability of the coolant outlet 94 and the EGR gas inlet96 can be exerted when the left flange portion 92 is fastened to thecoupling base 33 of the cylinder head 2 with bolts. Likewise, since theright flange portion 93 has the through holes 100 disposed below thecoolant inlet 95, above the EGR gas outlet 97, and to the right of aportion between the coolant inlet 95 and the EGR gas outlet 97, asealability of the coolant inlet 95 and the EGR gas outlet 97 can beexerted when the right flange portion 93 is fastened to the couplingbase 34 of the cylinder head 2 with bolts.

The gasket 98 is constituted by a lamination of two plates 98 a, 98 beach having through holes 101 to 103. The EGR gas passes through thethrough holes (EGR gas through holes) 101. The coolant passes throughthe through holes (coolant through holes) 102. Fastening bolts areinserted into the through holes (bolt through holes) 103. The gasket 98has such a shape that an inner peripheral edge at the EGR gas throughhole 101 is branched so as to be warped in the front-rear direction andis configured such that the open areas of the coolant through holes 102are larger than the open areas of the coolant outlet and inlet 94, 95.

In the gasket 98, the front plate 98 a has its inner peripheral edge atthe EGR gas through hole 101 being warped frontward, while the rearplate 98 b has its inner peripheral edge at the EGR gas through hole 101being warped rearward. The front plate 98 a and the rear plate 98 b arebonded by welding, so that the inner peripheral edge at the EGR gasthrough hole 101 has a Y-shaped cross-section. Since the innerperipheral edge at the EGR gas through hole 101 is warped in thefront-rear direction, front and rear surfaces of the inner peripheraledge at the EGR gas through hole 101 can be in tight contact with endsurfaces of the coupling bases 33, 34 and the flange portions 92, 93.Accordingly, a sufficient airtightness can be obtained.

The gasket 98 is configured such that the openings of the coolantthrough holes 102 is larger than those of the coolant outlet and inlet94, 95. Thus, the O-rings 99 are inserted in the coolant through holes102. Communication portions where the coolant outlet and inlet 94, 95 ofthe flange portions 92, 93 are in communication with the coolant relayfluid passages 38,39 of the coupling bases 33, 34 are hermeticallysealed by the O-rings 99 fitted in the coolant through holes 102 of thegasket 98.

The coupling bases 33, 34 of the cylinder head 2 have the coolant outletand inlet 94, 95 opened with steps, and thereby the openings of thecoolant outlet and inlet 94, 95 are given larger diameters than thefluid passage diameters of the coolant relay fluid passages 38, 39formed inside the coupling bases 33, 34. The O-rings 99 disposed to thecoolant outlet and inlet 94, 95 of the coupling bases 33, 34 are fittedon the outer circumferential sides of the coolant relay fluid passages38, 39. The O-rings 99 are inserted in the gasket 98, and also fitted inthe step portions of the coolant outlet and inlet 94, 95 in the couplingbases 33, 34. Thereby, the O-rings 99 are sandwiched between thecoupling bases 33, 34 and the flange portions 92, 93. When a coolantpasses inside the O-rings 99 made of an elastic material, the O-rings 99are deformed to expand outward and come into tight contact with thecoupling bases 33, 34 and the flange portions 92, 93, thus providing asealability for the coolant.

The ring-shaped O-ring 99 has its inner circumferential portion bulgingfrontward and rearward. A coolant passing through the innercircumferential portion of the O-ring 99 pushes the innercircumferential portion, so that its front and rear edges are deformedto protrude frontward and rearward. This brings the innercircumferential portion of the O-ring 99 into tight contact with thecoupling bases 33, 34 and the flange portions 92, 93. Thus, asealability for the coolant can be enhanced in the coupling portionwhere the cylinder head 2 is coupled to the EGR cooler 27.

The ring-shaped O-ring 99 whose inner circumferential portion is bulgedfrontward and rearward is shaped such that its inner circumferentialsurface has a recessed portion. The inner circumferential surface of theO-ring 99 is warped frontward and rearward so as to have a Y-shapedcross-section. A coolant passing through the inner circumferentialportion of the O-ring 99 pushes the inner circumferential portion, sothat its front and rear edges are further protruded frontward andrearward, to increase the degree of tight contact of the innercircumferential portion of the O-ring 99 with the coupling bases 33, 34and the flange portions 92, 93. Accordingly, a sealability for thecoolant can be enhanced in the coupling portion where the cylinder head2 is coupled to the EGR cooler 27.

A configuration of the two-stage turbocharger 30 will now be describedwith reference to FIG. 22 to FIG. 27, etc. As shown in FIG. 22 to FIG.27, the two-stage turbocharger 30 uses fluid energy of an exhaust gasdischarged from the exhaust manifold 4, to compress fresh air which thenflows into the intake manifold 3 of the cylinder head 2. The two-stageturbocharger 30 includes the high-pressure turbocharger 51 coupled tothe exhaust manifold 4, and the low-pressure turbocharger 52 coupled tothe high-pressure turbocharger 51.

The high-pressure turbocharger 51 is disposed on the left lateral sideof the exhaust manifold 4, while the low-pressure turbocharger 52 isdisposed above the exhaust manifold 4. The high-pressure turbocharger 51with a low capacity is disposed opposed to the exhaust manifold 4, whilethe low-pressure turbocharger 52 with a high capacity is disposed abovethe exhaust manifold 4 which is installled to the cylinder head 2 so asto protrude laterally leftward. This enables the exhaust manifold 4 andthe two-stage turbocharger 30 to be compactly arranged in a spaceexisting on the left lateral side of the cylinder head 2, and alsoenables a topmost portion of the two-stage turbocharger 30 to bepositioned lower than a topmost portion of the diesel engine 1. This cancontribute to downsizing of the diesel engine 1. In addition, thelow-pressure turbocharger 52 can be disposed close to the cylinder head2, and thus the two-stage turbocharger 30 can be fixed with a highrigidity.

The high-pressure turbocharger 51 includes the high-pressure turbine 53that is in communication with the exhaust gas outlet 44 of the exhaustmanifold 4, and the high-pressure compressor 54 that supplies compressedair to the intake manifold 3. The high-pressure compressor 54 is incommunication with the fresh air inlet 81 (see FIG. 17, etc.) of theintake throttle member 26 via an intercooler (not shown), and therebysupplies compressed air to the intake manifold 3 via the EGR device 24.The low-pressure turbocharger 52 includes the low-pressure turbine 55whose exhaust gas inlet is in communication with an exhaust gas outletof the high-pressure turbine 53 via an exhaust relay pipe, and thelow-pressure compressor 56 whose fresh air outlet is in communicationwith a fresh air inlet of the high-pressure compressor 54 via a freshair relay pipe. The low-pressure compressor 56 is disposed above thehigh-pressure turbine 53, the high-pressure compressor 54 is disposed onone of the front and rear sides relative to the high-pressure turbine53, and the low-pressure turbine 55 is disposed on the other of thefront and rear sides relative to the low-pressure compressor 56.

The exhaust gas outlet 44 of the exhaust manifold 4, which discharges anexhaust gas, is opened toward one of the left and right lateral sides.The exhaust gas inlet 57 of the high-pressure turbine 53 is openedtoward the exhaust manifold 4, and the exhaust gas outlet 58 of thehigh-pressure turbine 53 is opened frontward. The exhaust gas inlet 60of the low-pressure turbine 55 is opened downward, and the exhaust gasoutlet 61 of the low-pressure turbine 55 is opened frontward.

The exhaust gas outlet 44 of the exhaust manifold 4 and the exhaust gasinlet 57 of the high-pressure turbine 53, which are opposed to eachother, are flange-coupled with bolts, and thus the high-pressureturbocharger 51 is fixed on the left lateral side of the exhaustmanifold 4. The exhaust gas outlet 58 of the high-pressure turbine 53 isflange-coupled to one end (rear end) of the L-shaped high-pressureexhaust gas tube 59 (exhaust relay pipe) with bolts. The exhaust gasinlet 60 of the low-pressure turbine 55 is flange-coupled to the otherend (upper end) of the high-pressure exhaust gas tube 59 with bolts. Thelow-pressure turbocharger 52 is fixed on the upper side of thehigh-pressure turbocharger 51.

The high-pressure turbine 53 is flange-coupled to the exhaust manifold 4so that the high-pressure turbocharger 51 is supported with a highrigidity, and in this condition, the low-pressure turbine 55 isflange-coupled to an upper surface of the high-pressure exhaust gas tube59 that is flange-coupled to the front side of the high-pressureturbocharger 51. Thereby, the low-pressure turbocharger 52 can besupported from below by the high-pressure turbocharger 51. Since thelow-pressure turbocharger 52 is installed close to a position above theexhaust manifold 4, the center of gravity of the low-pressureturbocharger 52 is in the vicinity of a position above the positionwhere the exhaust manifold 4 is coupled to the high-pressureturbocharger 51. Accordingly, the two-stage turbocharger 30 can becompactly supported with a high rigidity in the vicinity of the dieselengine 1.

The high-pressure compressor 54 has a fresh air inlet port 63 (fresh airinlet) opened rearward, and has a fresh air supply port 64 (fresh airoutlet) opened downward. The low-pressure compressor 56 has a fresh airinlet port 66 (fresh air inlet) opened rearward, and has a fresh airsupply port 67 (fresh air outlet) protruding from the left lateral sideand then directed downward. The U-shaped low-pressure fresh air passagepipe 65 (fresh air relay pipe) has one end thereof fixed to the freshair inlet port 63 (fresh air inlet) of the high-pressure compressor 54,and has the other end thereof coupled to the fresh air supply port 67(fresh air outlet) of the low-pressure compressor 56.

The high-pressure compressor 54 and the low-pressure compressor 56 arecoupled by the U-shaped low-pressure fresh air passage pipe 65 disposedat the rear, and a front portion of the low-pressure turbocharger 52 canbe fixed to the high-pressure turbocharger 51 which is supported with ahigh rigidity by the exhaust manifold 4. The fresh air inlet port 66 andthe fresh air supply port 67 of the low-pressure compressor 56 areextended in the same direction (rearward), and can be easily coupled tothe air supply pipe 62 which is in communication with an air cleaner(not shown) and to the low-pressure fresh air passage pipe 65,respectively. This configuration can enhance a workability inassembling.

The low-pressure fresh air passage pipe 65 includes a metal pipe 65 aand a resin pipe 65 b. The metal pipe 65 a has its one endflange-coupled and bolt-fastened to the fresh air inlet port 66 of thehigh-pressure compressor 54. The resin pipe 65 b allows the other end ofthe metal pipe 65 a to communicate with the fresh air supply port 67 ofthe low-pressure compressor 56. Thereby, in the low-pressure fresh airpassage pipe 65, the metal pipe 65 a is fixed to the high-pressurecompressor 54 with a high rigidity, and the resin pipe 65 b allows thelow-pressure compressor 56 and the metal pipe 65 a to communicate witheach other while lessening an assembling error therebetween.

The fresh air supply port 67 of the low-pressure compressor 56 protrudeslaterally leftward from a left surface of the low-pressure compressor56, and then is directed upward toward the rear. This configurationenables the low-pressure fresh air passage pipe 65 (metal pipe 65 a) tobe bent with a large curvature. As a result, generation of a turbulentflow in the low-pressure fresh air passage pipe 65 can be suppressed, sothat the compressed air discharged from the low-pressure compressor 56can be smoothly supplied to the high-pressure compressor 54.

The blow-by gas recirculation device 19 for taking a blow-by gas in isinstalled above the cylinder head 2. The blow-by gas recirculationdevice 19 is placed on and fixed to the upper surface of the head cover18 that covers the upper surface of the cylinder head 2. A blow-by gasoutlet 70 disposed at the rear of the blow-by gas recirculation device19 is coupled to the air supply pipe 62 through the recirculation hose68, the air supply pipe 62 being coupled to the fresh air inlet port 66(fresh air inlet) of the low-pressure compressor 56. The air supply pipe62 is disposed between the low-pressure fresh air passage pipe 65 (freshair relay pipe) and the cylinder head 2.

The air supply pipe 62 is coupled to the rear side of the low-pressureturbocharger 52 which is an upper component of the two-stageturbocharger 30, and is disposed close to the cylinder head 2. Thus, thedistance between the air supply pipe 62 and the blow-by gasrecirculation device 19 disposed above the cylinder head 2 can beshortened. This makes it possible to shorten the recirculation hose 68to prevent the inside of the recirculation hose 68 from being freezedunder low-temperature environments. Since the air supply pipe 62 isdisposed in a space surrounded by the low-pressure fresh air passagepipe 65 and the cylinder head 2, the air supply pipe 62 can be preventedfrom being damaged by an external force which may be applied in acoupling portion coupled to a resin pipe which is connected to the aircleaner (not shown).

The fresh air supply port 64 of the high-pressure turbocharger 51, whichis opened downward, protrudes from a portion of a lower surface of thehigh-pressure compressor 54, the portion being on the cylinder head 2side. The high-pressure compressor 54 is coupled to the high-pressurefresh air passage pipe 71 which is in communication with the intercooler(not shown). The high-pressure compressor 54 supplies compressed air tothe intercooler through the high-pressure fresh air passage pipe 71. Thecoolant inlet pipe 22 which is opened laterally leftward is providedbelow the high-pressure compressor 54. The high-pressure fresh airpassage pipe 71 as well as coolant piping which is in communication withthe radiator (not shown) is arranged so as to extend to a rear portionof the left surface of the cylinder block 6, and thereby thehigh-pressure fresh air passage pipe 71 can be coupled to the coolantinlet pipe 22 and to the fresh air supply port 64 of the high-pressurecompressor 54. As a result, pipe routing for the coolant piping and thehigh-pressure fresh air passage pipe 71 can be collected, which cansimplify a piping structure in a main machine equipped with the dieselengine 1 and also can make an assembling work and a maintenance workeasy.

In the diesel engine 1, the coolant outlet pipe 23, the air supply pipe62, and the intake throttle member 26 are disposed above the cylinderhead 2 and on the cooling fan 9 side. In the main machine equipped withthe diesel engine 1, therefore, when the radiator (not shown), the aircleaner (not shown), and the intercooler (not shown) which use coolingair of the cooling fan 9 are disposed on the rear side of the coolingfan 9, coolant piping connected to the radiator and fresh air pipingcommunicating with the air cleaner and the intercooler can be shortened,and moreover works for connecting such piping can be performed together.As a result, an assembling work and a maintenance work in the mainmachine can be performed with ease, and in addition, component parts tobe coupled to the diesel engine 1 can be efficiently arranged in themain machine.

The exhaust gas outlet 58 of the high-pressure turbine 53 is providedwith a turbine discharge hole 58 a, a bypass hole 58 b, and a wastegatevalve 69. The turbine discharge hole 58 a discharges an exhaust gaswhich rotates a turbine wheel (not shown). The bypass hole 58 b allowsthe exhaust gas inlet 57 and the exhaust gas outlet 58 to communicatewith each other. The wastegate valve 69 opens and closes the bypass hole58 b. Arranging the turbine discharge hole 58 a and the bypass hole 58 bside-by-side in the exhaust gas outlet 58 of the high-pressure turbine53 enables whether to perform a compression operation by thehigh-pressure turbocharger 51 to be set in accordance with a rotationalfrequency of the diesel engine 1. Accordingly, with efficient use ofexhaust energy, the two-stage turbocharger 30 can stabilize the amountof fresh air to be supplied to the combustion chamber, and can reducethe amount of brack smoke discharge while increasing an engine output.

When the bypass hole 58 b of the high-pressure turbine 53 is opened, abypass path extending from the exhaust manifold 4 to the low-pressureturbine 55 is formed. Thus, only the high-pressure exhaust gas tube 59which allows the high-pressure turbine 53 and the low-pressure turbine55 to communicate with ach other needs to be arranged. Piping forbypassing purpose that allows the exhaust manifold 4 and thelow-pressure turbine 55 to communicate with each other needs not bearranged. This can simplify a piping structure in the two-stageturbocharger 30, and also can provide a large space around the two-stageturbocharger 30. It therefore is possible that, for example, an oilpressure pump (not shown) for a work machine and the engine startingstarter 20 are disposed one above the other at a location below thefront side of the two-stage turbocharger 30.

In the high-pressure turbocharger 51, a high-pressure working fluidsupply pipe 73 and a high-pressure working fluid return pipe 74 arecoupled to upper and lower portions of a center housing 72 which is acoupling portion where the high-pressure turbine 53 and thehigh-pressure compressor 54 are coupled to each other. Likewise, in thelow-pressure turbocharger 52, a low-pressure working fluid supply pipe76 and a low-pressure working fluid return pipe 77 are coupled to upperand lower portions of a center housing 75 which is a coupling portionwhere the low-pressure turbine 55 and the low-pressure compressor 56 arecoupled to each other.

The high-pressure working fluid supply pipe 73 has its lower endconnected to a coupling member 78 disposed on the left surface of thecylinder block 6, and its upper end coupled to an upper surface of thecenter housing 72 of the high-pressure turbocharger 51. A coupling joint79 is disposed on the upper surface of the center housing 72 of thehigh-pressure turbocharger 51, the coupling joint 79 allowing the upperend of high-pressure working fluid supply pipe 73 to communicate with alower end of the low-pressure working fluid supply pipe 76. An upper endof the low-pressure working fluid supply pipe 76 is coupled to an uppersurface of the center housing 75 of the low-pressure turbocharger 52.With this configuration, a working fluid flowing in an oil passagewithin the cylinder block 6 is supplied to the center housing 72 of thehigh-pressure turbocharger 51 through the high-pressure working fluidsupply pipe 73, and is supplied to the center housing 75 of thelow-pressure turbocharger 52 through the high-pressure working fluidsupply pipe 73 and the low-pressure working fluid supply pipe 76.

The high-pressure working fluid supply pipe 73 is laid between thehigh-pressure turbocharger 51 and the cylinder head 2 as well as thecylinder block 6 while detouring at the rear of the exhaust gas outlet44 of the exhaust manifold 4. The low-pressure working fluid supply pipe76 is laid in an L-shape extending along the upper surface of thehigh-pressure turbocharger 51 and the center housing 75 of thelow-pressure turbocharger 52. Such a piping layout surrounding thetwo-stage turbocharger 30 which is a high-rigidity component with theworking fluid supply pipes 73, 76 shortened enables the working fluid tobe efficiently supplied to the two-stage turbocharger 30 andsimultaneously prevents the working fluid supply pipes 73, 76 from beingdamaged by an external force.

The high-pressure working fluid return pipe 74 has one end (lower end)thereof coupled to the distal end (left-side distal end) of a couplingjoint 80 disposed on the left surface of the cylinder block 6, and theother end (upper end) thereof coupled to a lower surface of the centerhousing 72 of the high-pressure turbocharger 51. The low-pressureworking fluid return pipe 77 has one end (lower end) thereof coupled toone of branching upper ends of the coupling joint 80, and the other end(upper end) thereof coupled to a lower surface of the center housing 75of the low-pressure turbocharger 52. With this configuration, a workingfluid in the high-pressure turbocharger 51 and a working fluid in thelow-pressure turbocharger 52 flow through the low-pressure working fluidreturn pipes 74, 77 disposed below the center housings 72, 75, to bemerged at the coupling joint 80. A merged flow is returned to the oilpassage within the cylinder block 6.

The high-pressure working fluid return pipe 74 is laid so as to detourat the rear of the exhaust gas outlet 44 of the exhaust manifold 4. Thelow-pressure working fluid return pipe 77 is laid between thehigh-pressure turbocharger 51 and the cylinder head 2 as well as thecylinder block 6 while detouring at the front of the exhaust gas outlet44 of the exhaust manifold 4. Such a piping layout surrounding thetwo-stage turbocharger 30 which is a high-rigidity component with theworking fluid return pipes 74, 77 shorted enables the working fluid tobe efficiently supplied to the two-stage turbocharger 30 andsimultaneously prevents the working fluid return pipes 74, 77 from beingdamaged by an external force.

Configurations of the coolant pump 21 and the coolant inlet pipe 22 willnow be described with reference to FIG. 28, FIG. 29, and the like. Asshown in FIG. 28, FIG. 29, and the like, a coolant pump attaching part319 and an inlet pipe attachment pedestal 320 are provided so as toprotrude from a portion of the left surface of the cylinder block 6, theportion being relatively close to the rear surface of the cylinder block6. To the coolant pump attaching part 319, the coolant pump 21 (see FIG.2, etc.) is attached. To the inlet pipe attachment pedestal 320, thecoolant inlet pipe 22 (see FIG. 3, etc.) is attached. The coolant pumpattaching part 319 and the inlet pipe attachment pedestal 320 are formedintegrally with the cylinder block 6. A portion of the inlet pipeattachment pedestal 320 close to the rear surface is coupled to thecoolant pump attaching part 319. The coolant pump attaching part 319 andthe inlet pipe attachment pedestal 320 protrude in a direction away fromthe crankshaft 5, and can enhance the rigidity, the strength, and thecooling efficiency of the cylinder block 6.

The coolant pump 21 for circulating a coolant is fastened to the rearsurface 312 of the cylinder block 6 and to the coolant pump attachingpart 319 with bolts. The coolant pump 21 is roughly divided into a baseplate portion 331, a cover plate portion 332, and a pumping pulley 333.

The base plate portion 331 and the cover plate portion 332 have theirperipheral edge portions fixed in tight contact with each other bycovering bolts 347 that are inserted and fastened, from the cover plateportion 332 side, into five bolting through holes disposed in theperipheral edge portion of the base plate portion 331 and into throughholes of the cover plate portion 332 corresponding to the boltingthrough holes.

The coolant pump 21 is bolt-fastened to the cylinder block 6 such thatthe plate portions 331, 332 are clamped together by mounting bolts 348that are inserted in nine through holes disposed in each of theperipheral edge portions of the base plate portion 331 and the coverplate portion 332. Clamping with the mounting bolts 348 causes theperipheral edge portions of the base plate portion 331 and the coverplate portion 332 to be fixed in tight contact with each other, alsocauses a portion of the cylinder block 6 surrounding a coolant passageoutlet 327 and a portion of the coolant pump 21 surrounding a pumpsuction port 334 to be fixed in tight contact with each other, andfurther causes a portion of the cylinder block 6 surrounding a coolantinlet port 328 and a portion of the coolant pump 21 surrounding a pumpejection port 335 to be fixed in tight contact with each other. As forarrangement of the bolts 347, 348 along the peripheral edge portion ofthe coolant pump 21, one or two mounting bolts 348 are disposed betweenadjacent ones of the covering bolts 347, 347.

Since the base plate portion 331 and the cover plate portion 332 arecoupled to each other with the covering bolts 347, the coolant pump 21can be distributed as a single component, and moreover an attaching workin mounting the coolant pump 21 to the cylinder block 6 with themounting bolts 348 is easy.

The base plate portion 331, for example, includes a pump suction port334 and a pump ejection port 335, the pump suction port 334 beingconnected to the coolant passage outlet 327 which includes a portion ofthe coolant pump attaching part 319 and which is opened in a relativelyleft portion of the rear surface of the cylinder block 6, the pumpejection port 335 being connected to the coolant inlet port 328 which isopened in a relatively right portion of the rear surface of the cylinderblock 6.

The base plate portion 331 and the cover plate portion 332 have theirperipheral edge portions in tight contact with each other, to form anin-pump coolant passage 336 that connects the pump suction port 334 tothe pump ejection port 335. An annular seal member that surrounds thepump suction port 334, the pump ejection port 335, and the in-pumpcoolant passage 336 is disposed in a portion where the base plateportion 331 and the cover plate portion 332 are in tight contact witheach other. The cover plate portion 332 pivotally supports a pump shaft337 in a rotatable manner. An impeller is secured to one end portion ofthe pump shaft 337. The pumping pulley 333 is secured to the other endportion of the pump shaft 337.

A coolant passage inlet 329 is opened in the left surface of thecylinder block 6. The coolant passage inlet 329 is opened in the inletpipe attachment pedestal 320 which protrudes from the left surface. Anin-block coolant passage 338 (coolant passage) is formed inside thecylinder block 6. The in-block coolant passage 338 has a substantiallyL-shape that connects the coolant passage inlet 329 opened in the leftsurface to the coolant passage outlet 327 opened in the rear surface.

The inlet pipe attachment pedestal 320 has a pair of bolt holes onopposite sides of the coolant passage inlet 329. The coolant inlet pipe22 (coolant inlet member) having a coolant inlet 339 is detachablyfastened to the inlet pipe attachment pedestal 320 with bolts. Pipingleading to the coolant outlet of the radiator is connected to thecoolant inlet pipe 22. A coolant coming from the radiator is introducedinto the engine 1 through the coolant inlet pipe 22, flows through thein-block coolant passage 338 and the coolant pump 21, and then takeninto the cylinder block 6 from the coolant inlet port 328.

In the engine 1 of this embodiment, the coolant inlet pipe 22 having thecoolant inlet 339 is detachably attached to the coolant passage inlet329 which leads to the pump suction port 334 of the coolant pump 21.Accordingly, the position of the coolant inlet 339 can be changed justby changing the shape or the like of the coolant inlet pipe 22. Thisenables the position of the coolant inlet 339 of the coolant pump 21 tobe easily changed without any major design change or any increase inmanufacturing costs.

The coolant passage outlet 327 that supplies a coolant from the radiatorto the coolant pump 21 is disposed on one of the left and right sides ofthe cylinder block 6, while the coolant inlet port 328 that takes acoolant from the coolant pump 21 into the cylinder block 6 is disposedon the other of the left and right sides of the cylinder block 6. Thein-pump coolant passage 336 that connects the coolant passage outlet 327to the coolant inlet port 328 is disposed across a portion close to theleft surface of the cylinder block 6 and a portion close to the rightsurface of the cylinder block 6. With this configuration, a coolantpassing through the in-pump coolant passage 336 is cooled by cooling airsupplied from the cooling fan 9 (see FIG. 2) while the coolant is movingfrom the coolant passage outlet 327 to the coolant inlet port 328. Thecoolant can be cooled within the coolant pump 21 before being taken intothe cylinder block 6 from the coolant inlet port 328. Accordingly, thecooling efficiency of the engine 1 can be enhanced.

The configurations of respective parts of the present invention are notlimited to those of the illustrated embodiment, but can be variouslychanged without departing from the gist of the invention.

REFERENCE SIGNS LIST

1 engine

2 cylinder head

3 intake manifold

4 exhaust manifold

5 crankshaft

6 cylinder block

7 flywheel housing

8 flywheel

9 cooling fan

51 high-pressure turbocharger

52 low-pressure turbocharger

53 high-pressure turbine

54 high-pressure compressor

55 low-pressure turbine

56 low-pressure compressor

57 exhaust gas inlet

58 exhaust gas outlet

58 a turbine discharge hole

58 b bypass hole

59 high-pressure exhaust gas tube

60 exhaust gas inlet

61 exhaust gas outlet

62 air supply pipe

63 fresh air inlet port

64 fresh air supply port

65 low-pressure fresh air passage pipe

65 a metal pipe

65 b resin pipe

66 fresh air inlet port

67 fresh air supply port

68 recirculation hose

69 wastegate valve

70 blow-by gas outlet

71 high-pressure fresh air passage pipe

72 center housing

73 high-pressure working fluid supply pipe

74 high-pressure working fluid return pipe

75 center housing

76 low-pressure working fluid supply pipe

77 low-pressure working fluid return pipe

78 coupling member

79 coupling joint

80 coupling joint

1. An engine device including: an exhaust manifold and an intakemanifold, the exhaust manifold being disposed on one of left and rightsides of a cylinder head, the intake manifold being disposed on anotherone of the left and right sides of the cylinder head; and a turbochargerconfigured to use fluid energy of an exhaust gas discharged from theexhaust manifold, to compress fresh air to be flowed into the intakemanifold, wherein the turbocharger is constituted by a two-stageturbocharger including a high-pressure turbocharger coupled to theexhaust manifold and a low-pressure turbocharger coupled to thehigh-pressure turbocharger, the high-pressure turbocharger beingdisposed on one of left and right lateral sides of the exhaust manifold,and the low-pressure turbocharger being disposed above the exhaustmanifold; the high-pressure turbocharger includes a high-pressureturbine and a high-pressure compressor, the high-pressure turbine beingin communication with an exhaust gas outlet of the exhaust manifold, andthe high-pressure compressor being configured to supply compressed airto the intake manifold; the low-pressure turbocharger includes alow-pressure turbine and a low-pressure compressor, the low-pressureturbine having an exhaust gas inlet that is in communication with theexhaust gas outlet of the high-pressure turbine through an exhaust relaypipe, and the low-pressure compressor having a fresh air outlet that isin communication with a fresh air inlet of the high-pressure compressorthrough a fresh air relay pipe; the low-pressure compressor is disposedabove the high-pressure turbine, the high-pressure compressor isdisposed on one of front and rear sides relative to the high-pressureturbine, and the low-pressure turbine is disposed on the other of thefront and rear sides relative to the low-pressure compressor; thehigh-pressure compressor has the fresh air inlet that is opened towardone of front and rear sides thereof, and has a fresh air outlet that isopened downward; the low-pressure compressor has a fresh air inlet thatis opened toward one of front and rear sides thereof, and a fresh airoutlet that protrudes from one of left and right lateral sides thereofand then is directed toward the one of front and rear sides; one end ofthe fresh air relay pipe having a U-shape is fixed to the fresh airinlet of the high-pressure compressor, the other end of the fresh airrelay pipe being coupled to the fresh air outlet of the low-pressurecompressor; and the fresh air inlet and the fresh air outlet of thelow-pressure compressor are disposed toward the same direction.
 2. Theengine device according to claim 1, wherein: the fresh air relay pipeincludes a metal pipe and a resin pipe, the metal pipe having one endthereof flange-coupled and bolt-fastened to the fresh air inlet of thehigh-pressure compressor, the resin pipe allowing anther end of themetal pipe to communicate with the fresh air outlet of the low-pressurecompressor.
 3. The engine device according to claim 1, wherein: theexhaust manifold has an exhaust gas outlet configured to discharge anexhaust gas, the exhaust gas outlet being opened toward one of left andright lateral sides of the exhaust manifold, the high-pressure turbinehas an exhaust gas inlet that is opened toward the exhaust manifold, andhas an exhaust gas outlet that is opened toward another one of front andrear sides of the high-pressure turbine, the low-pressure turbine has anexhaust gas inlet that is opened downward, and has an exhaust gas outletthat is opened toward another one of front and rear sides of thelow-pressure turbine, the exhaust gas outlet of the exhaust manifold andthe exhaust gas inlet of the high-pressure turbine that are opposed toeach other are coupled, to fix the high-pressure turbocharger on one ofleft and right lateral sides of the exhaust manifold, and the exhaustgas outlet of the high-pressure turbine is fixed to one end of theexhaust relay pipe having an L-shape, the exhaust gas inlet of thelow-pressure turbine is fixed to the other end of the exhaust relaypipe, and the low-pressure turbocharger is fixed above the high-pressureturbocharger.
 4. (canceled)
 5. The engine device according to claim 1,wherein: a blow-by gas recirculation device configured to take a blow-bygas in is provided on the cylinder head, and a blow-by gas outletdisposed on one of front and rear sides of the blow-by gas recirculationdevice is coupled to an air supply pipe through a recirculation hose,the air supply pipe being coupled to the fresh air inlet of thelow-pressure compressor, and the air supply pipe is disposed between thefresh air relay pipe and the cylinder head.
 6. The engine deviceaccording to claim 1, wherein: the exhaust gas outlet of thehigh-pressure turbine is provided with a turbine discharge hole, abypass hole, and a wastegate valve, the turbine discharge hole beingconfigured to discharge an exhaust gas for rotating a turbine wheel, thebypass hole allowing the exhaust gas inlet and the exhaust gas outlet tocommunicate with each other, and the wastegate valve being configured toopen and close the bypass hole.